This invention relates to induction furnaces and more particularly to the upper rings used in such furnaces.
An induction furnace employs electromagnetic energy to induce electrical currents to flow within a charge of metal or metal alloy. The electrical resistance of the metal produces heat as a natural consequence of the induced currents flowing in the metal. The combination of applied electrical power and frequency can be chosen to create sufficient heat within the metal to cause it to melt. The molten metal can then be poured into molds or otherwise used to produce a wide variety of metal products.
Referring now to FIG. 1 there is shown the cross-section of a traditional induction furnace 10. The basic elements of induction furnace 10 include an electromagnetic induction coil 12, a crucible or vessel 14 having a lining 28 of refractory material and a structure 16 for supporting the induction coil and vessel. The induction coil 12 comprises an electrical conductor of sufficient size and current capacity to produce the magnitude of magnetic flux necessary to induce large currents in the metal charge. The magnetic flux represents the lines of force of a magnetic field. The magnetic field emanates from the furnace coil and penetrates the charge material inside the crucible 14, causing induced current to flow in the charge resulting in the generation of heat culminating in the melting of the charge material.
Magnetic yokes 18 are placed at periodic intervals around the outside of the induction coil 12 and are pressed inward by means of clamping bolts 20 to hold the induction coil 12 in place. The yokes 18 provide radial support to the coil 12, the crucible 14, and the charge material contained therein. In addition, the yokes 18 prevent the stray flux surrounding the outside of the coil from entering the frame 16 of the furnace and causing unwanted heating of the structure. A further function of yokes 18 is to minimize exposure of operating personnel to stray magnetic fields in order to comply with applicable health and safety rules.
The coil 12 is held in place axially by means of concrete castings 22 and 24 in the form of a ring that are typically cast in place after the coil 12 and yokes 22 are installed. As is well known, lower ring 24 of traditional furnace 10 has straight outer walls. Also shown in FIG. 1 are the cover 25, the quick lining release push-out plug 26, Ground electrodes 27 and spout 29.
In some of the larger traditional furnaces there is axial compression on the coil 12 from the bottom only of those furnaces. Since in those furnaces the upper end of the coil 12 does not receive direct axial compression the longevity of the coil may be compromised under certain severe conditions of operation.
Although traditional furnace 10 has proven to be durable it may be necessary during the life of the furnace to change coil 12 or the cast in place upper ring 22 from time to time at an interval from 6 months to several years depending on severity of service. That change is a time consuming and lengthy procedure usually requiring at least several days and for larger furnaces up to two weeks. During that time period there is a loss of production from the furnace. Therefore it is desirable to reduce the amount of time and labor and thus the cost of replacing the coil or the upper ring and also allow a future replacement of either or both elements to be easily made. As can be appreciated a reduction in the amount of time to replace the coil or upper ring can add to production from the furnace. The structure and method of the present invention provides these benefits as well as benefits in the construction of new furnaces.
A method for replacing an upper ring casted on an induction furnace comprising replacing the upper ring casted on the furnace with a holder having a cured ring that is cast as one piece in the holder off of the furnace.
A method for replacing an upper ring casted on an induction furnace comprising:
a) casting an upper ring as one piece in a holder off of the furnace; and
b) replacing the upper ring casted on the furnace with the holder having therein the one piece upper ring after the one piece upper ring is cured.
A method for replacing an upper ring of an induction furnace comprising:
a) removing the upper ring;
b) casting an upper ring as one piece in a holder off of the furnace; and
c) placing the holder having the one piece upper ring therein on the furnace after the one piece upper ring is cured.
A method for replacing components in an induction furnace, the furnace comprising an upper ring, an induction coil, yokes, a lower ring and a frame, the method comprising:
a) removing the upper ring, the lower ring, the induction coil and the yokes from the furnace;
b) casting an upper ring as one piece in a holder off of the furnace;
c) returning the yokes to the furnace;
d) replacing the removed induction coil with an induction coil modified to include cooling turns at the top of the induction coil;
e) tightening the yokes while ensuring that the modified coil remains centered and plumb within the furnace frame;
f) casting a new lower ring on the furnace; and
g) installing the holder on the furnace after the one piece upper ring is cured.
An induction furnace comprising:
a) a crucible having a refractory lining for holding a charge of metal or a metal alloy;
b) an electromagnetic induction coil surrounding the crucible; and
c) upper and lower castable rings for holding the coil axially, the lower ring cast on the furnace and the upper ring in a holder and cast as one piece in the holder off of the furnace.
An upper ring for an induction furnace that comprises a holder in which the ring is cast in one piece, the holder for mounting the cast one piece upper ring on the furnace.